By SCOTT SAYARE

Published: April 12, 2013

PARIS — The French Senate on Friday approved a bill to allow same-sex couples to wed and adopt children, leaving France poised to join the small group of nations that have fully legalized gay marriage, despite an unexpectedly vocal campaign by conservative opponents.

A final vote on the legislation, which figured among the campaign promises of President François Hollande, has been scheduled for next week in the lower house of Parliament, where the Senate’s minor amendments are expected to easily pass. Mr. Hollande’s Socialist Party holds a strong majority in the lower house, which approved an earlier version of the text in February.

Should the bill pass, parliamentary conservatives have vowed to challenge its constitutionality, though precedent suggests that a rejection by the Constitutional Council, which rules on such matters, would be unlikely.

The French debate over legalizing gay marriage comes as the Supreme Court of the United States is examining a law that prohibits it; one possible ruling in that case, concerning California’s ban on same-sex marriage, would require all 50 states to allow such unions. Same-sex marriage has been legalized in several American states, some areas of Brazil and Mexico and 12 countries, half of them in Europe.

In France, the left has broadly supported the bill on gay marriage, which many supporters prefer to call “marriage for all.” The country’s largest conservative party, the center-right Union for a Popular Movement, has opposed it. There have been a few dissonant voices at both ends of the political spectrum. On Friday, the Senate vote fell largely along partisan lines, 179 to 157.

“You have consolidated and reinforced the republican pact,” Justice Minister Christiane Taubira told the Senate after the vote. In opening marriage to same-sex couples, Ms. Taubira said, “we are simply recognizing their full citizenship.”

There has been marked opposition, however, in a country that remains largely Roman Catholic, with deeply rooted conservative convictions in much of the populace. Opponents of the bill, many of them rallying under a movement called La Manif Pour Tous, or Protest for All, have marched in the hundreds of thousands in Paris and across the country in recent months. Organizers have called for a mass protest next month.

Christian, Jewish and Muslim religious leaders have also called upon the faithful to protest the legislation, which many opponents cast as a danger for future generations of children who could be raised by homosexual parents. Indeed, opposition has largely focused on the provision, now approved by both houses of Parliament, that would allow same-sex couples to adopt.

It is legal in France for someone who is gay or lesbian to adopt a child, but gays and lesbians may not adopt as couples, with equal parental rights.

A version of this article appeared in print on April 13, 2013, on page A10 of the New York edition with the headline: French Senate Approves Same-Sex Marriage Bill.